Control for die pads and presses



Feb. 12, 1963 F. M. WILLIAMSON 3,

CONTROL FOR DIE PADS AND PRESSES Filed June 1'7. 1960 3 Sheets-Sheet 1 Feb. 12, 1963 F. M. WILLIAMSON 3,077,344

CONTROL FOR DIE PADS AND PRESSES Filed June 17, 1960 5 Sheets-Sheet 2 M2, ma 4 5 I INVENTOR.

Feb. 12, 1963 F. M. WILLIAMSON 3,077,344

CONTROL FOR DIE PADS AND PRESSES Filed June 17. 1960 3 Sheets-Sheet 3 /d2, 406 I W/ A IN V EN TOR. f dg/ MWZZZ- kms /7.

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drama I This invention relates to a press of the type employing a movable die pad which is engaged by the work and more particularly to a hydraulic control system for the die pad, which is designed to delay the return movement of the die pad to its extended position upon opening of the press. In a system of this type, the die pad is backed up by a hydraulic cushion which consists of a piston working within a cylinder and a valve arrangement which is designed to offer a predetermined resistance to downward movement of the die pad upon closing of the press and to then force the hydraulic fluid back into the cylinder to raise the die pad to its extended position upon opening of the press. In many instances it is desirable to delay such return movement of the die pad, and the present invention is directed to a control system of this type.

A principal object of the invention is to provide a hydraulic control system for a die pad in a press designed to delay the return movement of the die pad upon opening of the press.

Another object of the invention is to provide a die pad which is returned to its extended position upon opening of the press by fluid under pressure, and a control for temporarily blocking the flow of the pressure fluid to the die pad upon opening of the press.

Other and further objects of the invention will be apparent from the following description and claims and may be understood by reference to the accompanying drawings, of which there are three sheets, which by way of illustration show preferred embodiments of the invention and what I now consider to be the best mode of applying the principles thereof. Other embodiments of the invention may be used without departing from the scope of the present invention as set forth in the appended claims.

In the drawings:

FIG. 1 is a somewhat schematic sectional view illustrating a part of the hydraulic control system of this invention;

FIG. 2 is an elevational view of the valve block forming a part of the system;

FIG. 3 is a sectional view taken on line 33 of FIG. 2;

FIG. 4 is a sectional view taken on line 4-4 of FIG. 3;

FIG. 5 is a sectional view illustrating a modified form of the invention;

FIG. 6 is a sectional view taken on and FIG. 7 illustrates a switch operated by some moving part of the press for operating the time-delay valve illustrated in FIGS. 5 and 6.

The invention may be embodied in a press which includes an upper die 10 and a lower die 12 supported on a fixed bolster 14, with the work 16 supported on the lower die 12 and engaging a reciprocable die pad 18. The die pad 18 is normally maintained in its upper or extended position by a piston 20 which is reciprocable within a cylinder 22 supplied with hydraulic fluid such as oil under pressure through a line 24.

When the press closes, the die pad 18 is forced downwardly against the piston 20 and the pressure fluid within the cylinder 22 resists such movement to utter a predetermined resistance to the movement of the die pad in a manner to be explained hereinafter. When the press is opened the pressure fluid is forced back into the cylinder line 6-6 of FIG. 5;

3,677,344 Patented Feb. 12, 1963 ice to raise the piston 20 and the die pad 18 into position for the succeeding operation of the press.

The hydraulic control system includes a supply tank 30 having a line 32 leading to a valve block 34 which is provided with a bore 36 intersected by a passage 38 which communicates with the passage 24 through a conduit 40. A pressure relief valve 42 normally closes the communication between the passages 36 and 38 in the valve block. The valve 42 is maintained. in its closed position by a spring 44 which is confined between the valve 42 and a piston 46 which is engaged by an adjustable screw 48 by means of which the pressure at which the valve 42 will open may be regulated as desired. When the upper die It) descends to eiiect the working stroke of the press, the die pad 18 is forced downwardly against the resistance olfered by the pressure fluid trapped beneath the piston 20. When this pressure exceeds a predetermined amount, the pressure relief valve will open to allow the oil to flow past it, back to the supply tank 30 through the passage 36 and line 32.

The pad delay arrangement is illustrated in FIGS. 3 and 4 and includes a valve bore 50 in the valve block 34 containing spool valves 52 and 54 which are urged to their left-hand position, as viewed in FIGS. 3 and 4 by a spring 56 which is confined within the bore: 56 and reacts against the spool valve 54 and a stop 58 disposed within the bore Sit and engaged by a screw 60 which may be adjusted to regulate the extent of the time delay.

A valve 62 attached to the valve block 34 includes a recess 64 containing a sleeve 66 within which a valve 68 is disposed. The cylinder 70 defined by the sleeve 68 com municates with the valve bore 50 and, in the normal position of the time-delay valve illustrated in. FIG. 3, the valve 68 is engaged by the spool 52 and held in its lefthand position within the cylinder 70 by the spring 56.

A passage 72 leads from the passage 38 to a passage 74 in the valve body 62. The end of the passage 74 is closed by a check valve 76 arranged within a recess 78. A passage 80 leads from the passage 74 to the recess 64, and the sleeve 66 is provided with a peripheral groove 82 and a radial opening 84 by means of which the pres sure fluid is supplied to an annular groove 86 on the valve 68. The valve 68 is provided with a radial passage 88 and an axial passage 90 by means of which the pressure fluid is conveyed to the inner end of the recess 64 to move the valve 68 and the spools 5'2 and 54 to their right-hand positions in which the stem 92 of the spool 54 engages the stop 58. as shown in FIG. 4. 7

Upon closing of the press, the pressure fluid discharged from the cylinder 22 is forced through line 4i into passage 38 and into the passage 72 which is connected into the passage 38 ahead of the pressure relief valve 42. The pressure fluid is thus forced through passages 72, 74- and 8t into the annular groove 82 and through radial opening 84 into groove 86 and through passages 88 and 90 to the left-hand end of the recess 64 to force the valve 68 and the spools 52 and 54 against the stop 58. As the valve 63 moves to the right, the groove 86 will pass the radial opening 84 until the lef-hand end of the valve 68 closes off the opening 84. However, the pressure fluid then flows past the check valve 76 and through a passage 94 to an annular groove 96 on sleeve 66 and into the cylinder 70 through a radial opening 93 in the sleeve 66 so that the valve will continue its movement after the radial opening 84 is cut oii.

The valve block 34 is provided with passages 100 and 162 which communicate with the bore 36. A passage 194 communicates with the passage 1% and with the bore 59 between the valve spools 52 and 54. A passage 196 communicates with the passage 1G2 and with the valve bore 5% on the right-hand side of the spool 54. A

passage 108 also intersects the bore opposite the point at which the passage 1% intersects the bore t) and a passage 110 intersects the bore 5t) opposite the passage 1%. The passages 1G8 and 110 communicate with passages 112 and 114, respectively, which intersect a passage 116 which communicates the passages 112 and 114 with the bore 38. Check valves 113 and 12d normally close the passages 112 and 114.

When the press is opened and the pressure in the system thereby reduced, the fluid under pressure in the tank 30 is forced through bore 36 and through passages 1 32 and 106, bore 59, passages 11% and lid, past check valve 129 into the bore 33, and back to cylinder 22 through line 40. The pressure fluid is also returned through passages ltltl and 104, valve bore 5%, passages 16$ and 112, past check valve 118 into the bore 38, and back to the cylinder 22. This return movement of the die pad 18 would normally be effected substantially immediately upon opening of the press, but the time-delay valve is effective to delay such return movement of the die pad since the valve spools 5'2 and 54 are shifted to the right, as described, during the working stroke of the press and cut off the passages 164, 1%, 198 and Elli. The oil trapped in the cylinder id is allowed to escape slowly past a bleeder valve 13%, which is disposed in the passage 94, and through passages E32 and 134 back to the passage 74 and through passage '72 into the bore 38. As the valve 68 moves to the left and the groove 86 is again brought into communication with the radial passage 34, the pressure fluid may then be returned through passages 90 and 88 in the valve 63 and through passages 84 and 30 back to the line '74. As the valve d3 returns, the valve spools 52 and 54- open the passages 16 2, rss, 1% and 1.1% so that the fluid under pressure from the tank 3% may be returned to the cylinder 22 in the manner described to return the die pad to its extended position, thereby stripping the work from the die.

The bleeder valve 13% may be set to provide the maximum time delay, and the adjusting screw 6% may be employed for varying the length of the stroke of the valve 68 so that the time delay will be determined by the amount of oil that must be displaced from the cylinder 70. A groove 136 leading to passage 1&8 prevents fluid from being trapped in the valve bore 5% and a similar groove 138 communicating with passage 1% prevents the pressure fluid from being trapped in the right-hand end of the valve bore 5%. In the modification illustrated in FIGS. 5, 6 and 7, the valve block 34 and the valve spool arrangement is the same as in the modification already described. In this form of the invention the control valve 62 is replaced by a solenoid 146 having a core 142 which engages the valve spool 52. When the solenoid is tie-energized, the pressure fluid is forced past the check valves 113 and 120 through the passages described to effect return movement of the die pad. When the solenoid is energized, the core 134 engages the valve spool 52 to shift the valve spools into the position shown in FIG. 6 in which the ports 1%, 1%, 103 and 110 are closed. The solenoid 140 may be energized by the closing of a switch 144, which includes a movable switch arm 145 engaged by a cam 148 on the crank 15% or any other moving part of the press. The extent of the time delay in this case is determined by the length of the cam 14d and, as soon as the switch arm 146 is disengaged by the cam 14-8, the switch 144 will open to de-energize the solenoid and allow spring 56 to return the valve spools 52 and 54 to open the passages 104, 106, 188 and 110.

The control of this application is an improvement over that disclosed in my prior Patents 2,890,669, 2,901,238, 2,924,446, and 3,059,914, and this application is a continuation-in-part of my prior copending application Serial No. 768,889, filed October 22, 1958, for Hydraulic Press Ram Cushion.

While I have illustrated and described preferred embodiments of my invention, it is understood that these are capable of modification, and I therefore do not Wish to be limited to the precise details set forth but desire to avail myself of such changes and alterations as fall within the purview of the following claims.

I claim:

1. in a press having a rcciprocable die pad engaged by the Work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect; return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one" direction, a return line leading from said tank back to said passage on the inlet side of said pressure relief valve through which the pressure fluid is returned from said tank to said cylinder to effect return movement of said pad upon opening of the press ram, a valve for opening and closing said return line, means urging said valve to a position in which said return line is open, means including a chamber and a piston therein operable responsive to the discharge of pressure fluid from said cylinder upon closing of the press ram to move said valve to a position closing said return line, means for trapping the pressure fluid in said chamber to hold said valve in said last-mentioned position, an outlet from said chamber communicating with said passage on the inlet side of said pressure relief valve, a bleeder valve in said outlet for restricting the escape of pressure fluid from said chamber through said outlet into said passage to delay return movement of said valve and opening of said return line thereby to delay said return movement of said die pad upon opening of the press.

2. Apparatus according to claim 1 including a stop for determining the stroke of said piston in said chamber, and means for adjusting said stop to regulate the quantity of pressure fluid trapped in said chamber.

3. In a press having a reciprocable die pad engaged by the Work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid under the pressure in said tank is returned from said tank to said cylinder to effect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, a spring in one end of said bore and reacting on said spool valve for urging said spool valve to one of said positions in which said return line is open, means operable upon closing of the press ram for shifting said spool valve to its other position closing said return line, and timing means associated with said lastmentioned means for holding said spool valve in said last-mentioned position for a predetermined time thereby to delay opening of said return line and return move ment of said die pad upon opening of the press, said bore having a slot therein between said one end thereof and said return line and forming a bypass around said spool valve.

4. In a press having a reciprocable die pad engaged by the work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press rain, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid under the pressure in said tank is returned from said tank to said cylinder to effect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, means for urging said spool valve to a position in which said return line is open, means operable upon closing of the press ram for shifting said spool valve to its other position closing said return line, and timing means associated with said last-mentioned means for holding said spool valve in said last-mentioned position for a predetermined time thereby to delay opening of said return line and return movement of said die pad upon opening of the press, said means for shifting said valve comprising a solenoid having a core reacting on one end of said valve, and said timing means comprising an electrical switch in the solenoid circuit and a cam driven with the press and operable for opening and closing said switch in timed relation to the stroke of the press ram.

5. Apparatus according to claim 3 wherein said means for shifting said valve comprises a hydraulically actuated piston engaging said valve and movable in a direction to shift said valve by the pressure fluid discharged from said cylinder upon closing of the press ram.

6. Apparatus according to claim 3 wherein said timing means comprises a chamber, passage means for supplying pressure fluid discharged from said cylinder to said chamer upon closing of the press ram, a one-way valve in said passage means, a discharge outlet from said chamber communicating with said passage on the inlet side of said pressure relief valve, and a bleeder valve in said outlet for restricting the escape of fiuid from said chamber through said outlet into said passage.

7. Apparatus according to claim 6 including means for adjusting said bleeder valve to regulate the rate of flow past said bleeder valve.

8. In a press having a reciprocable die pad engaged by the work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank back to said passage on the inlet side of said pressure relief valve and through which the pressure fluid is returned from said tank to said cylinder to effect return movement of said pad upon opening of tie press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore for opening and closing said return line, a control valve having a chamber therein, a piston in said chamber arranged to react against one end of said spool valve, means urging said spool valve against said valve piston to a position in which said return line is open, means communicating said chamber with said passage for delivering pressure fluid discharged from said cylinder to said chamber upon closing of the press ram to move said valve piston and spool valve to close said return line, said valve piston being adapted to close said communication between said passage and chamber during said movement, a by-pass connecting said passage and said chamber, a one-way valve in said by-pass through which pressure fluid is supplied to said chamber after the communication between said passage and cham ber is closed off by said valve piston for trapping the pressure fluid in said chamber, passage means leading from the downstream side of said one-Way valve back to said passage on the inlet side of said pressure relief valve, a bleeder valve in said passage means for restricting the escape of pressure fluid from said chamber to delay return movement of said spool valve and opening of said return line thereby to delay said return movement of said die pad upon opening of the press rain 9. In a press having a reciprocable die pad engaged by the work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to efiect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passagethrough said valve block havingone end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid under the pressure in said tank is returned from said tank to said cylinder to etlect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, means for urging said spool valve to one of said positions, means operable for applying a force for a predetermined time to said spool valve for shifting said spool valve to its other position, and a cam associated with said last-mentioned means and rotatable in accordance with movement of said press ram for controlling said last-mentioned means thereby to effect return movement of said die pad upon opening of the press ram.

10. A press according to claim 9 wherein said return line includes first and second sets of hydraulic fluid ports in said bore, two of said ports being disposed in parallel and communicating with said tank and two other of said ports being disposed in parallel and communicating with said die pad cylinder, said spool valve including a series of separate spool valve members, one for each of said sets of fluid ports.

11. In a press having a reciprocable die pad engaged by the work so as to be moved in one direction by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid is returned from said tank to said cylinder to effect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, means for urging said spool valve to one of said positions, and means operable in accordance with movement of said press ram for applying pressure to said spool valve for shifting it to its other position thereby to govern the return movement of said die pad upon opening of the press ram, said return line including first and second sets of hydraulic fluid ports in said bore, two of said ports being disposed in parallel and communicating with said tank and two other of said ports being disposed in parallel and communicating with said die pad cylinder, said spool valve including a series of separate spool valve members, one for each of said sets of fluid ports.

12. In a press having a reciprocable die pad engaged by the work so as to be moved in one direction by and upon closing of the press rain and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fluid under pressure, a passage through said valve block having one end communicating with said cylinder and its other end communicating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid under the pressure in said tank is returned from said tank to said cylinder to eilect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, means for urging said spool valve to a position in which said return line is open, means operable upon closing of the press ram for shifting said spool valve to its other position closing said return line, and timing means associated with said lastmentioned means for holding said spool valve in said last-mentioned position for a predetermined time thereby to delay opening of said return line and return movement of said die pad upon opening of the press, said return line including first and second sets of hydraulic fluid ports in said bore, two of said ports being disposed in parallel and communicating with said tank and two other of said ports being disposed in parallel and communicating with said die pad cylinder, said spool valve including a series of separate spool valve members, one for each of said sets of fluid ports.

13. In a press having a ram and a reciprocable die pad engaged by the work so as to be moved in one di rection by and upon closing of the press ram and including a hydraulic cushion to resist said movement of the pad and to effect return movement of the pad upon opening of the press ram, said hydraulic cushion including a cylinder and a piston therein reacting against said pad, a valve block, a supply tank for fiuid under pressure, a passage through said 'valve block having one end communicating with said cylinder and its other end com municating with said supply tank, an adjustable spring loaded pressure relief valve in said passage for maintaining a predetermined pressure in said cylinder upon movement of said pad in said one direction, a return line leading from said tank to said passage on the inlet side of said pressure relief valve through which the hydraulic fluid is returned from said tank to said cylinder to eflect return movement of said pad upon opening of the press ram, a bore in said valve block intersecting said return line, a spool valve reciprocable in said bore to open and closed positions for opening and closing said return line, means for urging said spool valve to one of said positions, and means operable in accordance with movement of said press ram for applying pressure to said spool valve for shifting it to its other position thereby to govern the return movement of said die pad upon opening of the press ram, said means for shifting said valve comprising an electric circuit including a solenoid having a core reacting on one end of said valve, and timing means comprising an electrical switch in the solenoid circuit and a cam driven with the press and operable for opening and closing said switch in timed relation to the stroke of the press ram.

14. Apparatus according to claim 9 wherein said means for shifting said spool valve comprises a solenoid having a core reacting on one end of said spool valve, said solenoid being arranged in a circuit having an electrical switch arranged to be opened and closed by said cam in timed relation with the stroke of the press ram.

References Cited in the file of this patent UNITED STATES PATENTS 1,757,737 Rode May 6, 1930 1,849,691 Rode Mar. 15, 1932 2,901,238 Williamson Aug. 25, 1959 

3. IN A PRESS HAVING A RECIPROCABLE DIE PAD ENGAGED BY THE WORK SO AS TO BE MOVED IN ONE DIRECTION BY AND UPON CLOSING OF THE PRESS RAM AND INCLUDING A HYDRAULIC CUSHION TO RESIST SAID MOVEMENT OF THE PAD AND TO EFFECT RETURN MOVEMENT OF THE PAD UPON OPENING OF THE PRESS RAM, SAID HYDRAULIC CUSHION INCLUDING A CYLINDER AND A PISTON THEREIN REACTING AGAINST SAID PAD, A VALVE BLOCK, A SUPPLY TANK FOR FLUID UNDER PRESSURE, A PASSAGE THROUGH SAID VALVE BLOCK HAVING ONE END COMMUNICATING WITH SAID CYLINDER AND ITS OTHER END COMMUNICATING WITH SAID SUPPLY TANK, AN ADJUSTABLE SPRING LOADED PRESSURE RELIEF VALVE IN SAID PASSAGE FOR MAINTAINING A PREDETERMINED PRESSURE IN SAID CYLINDER UPON MOVEMENT OF SAID PAD IN SAID ONE DIRECTION, A RETURN LINE LEADING FROM SAID TANK TO SAID PASSAGE ON THE INLET SIDE OF SAID PRESSURE RELIEF VALVE THROUGH WHICH THE HYDRAULIC FLUID UNDER THE PRESSURE IN SAID TANK IS RETURNED FROM SAID TANK TO SAID CYLINDER TO EFFECT RETURN MOVEMENT OF SAID PAD UPON OPENING OF THE PRESS RAM, A BORE IN SAID VALVE BLOCK INTERSECTING SAID RETURN LINE, A SPOOL VALVE RECIPROCABLE IN SAID BORE TO OPEN AND CLOSED POSITIONS FOR OPENING AND CLOSING SAID RETURN LINE, A SPRING IN ONE END OF SAID BORE AND REACTING ON SAID SPOOL VALVE FOR URGING SAID SPOOL VALVE TO ONE OF SAID POSITIONS IN WHICH SAID RETURN LINE IS OPEN, MEANS OPERABLE UPON CLOSING OF THE PRESS RAM FOR SHIFTING SAID SPOOL VALVE TO ITS OTHER POSITION CLOSING SAID RETURN LINE, AND TIMING MEANS ASSOCIATED WITH SAID LASTMENTIONED MEANS FOR HOLDING SAID SPOOL VALVE IN SAID LAST-MENTIONED POSITION FOR A PREDETERMINED TIME THEREBY TO DELAY OPENING OF SAID RETURN LINE AND RETURN MOVEMENT OF SAID DIE PAD UPON OPENING OF THE PRESS, SAID BORE HAVING A SLOT THEREIN BETWEEN SAID ONE END THEREOF AND SAID RETURN LINE AND FORMING A BY-PASS AROUND SAID SPOOL VALVE. 